The embodiments described herein relate to an apparatus for controlling gas exchange processes in a fluid processing machine, and more particularly to a valve and cylinder head assembly for an internal combustion engine.
Many fluid processing machines, such as, for example, internal combustion engines, compressors, and the like, require accurate and efficient gas exchange processes to ensure optimal performance. For example, during the intake stroke of an internal combustion engine, a predetermined amount of air and fuel must be supplied to the combustion chamber at a predetermined time in the operating cycle of the engine. The combustion chamber then must be sealed during the combustion event to prevent inefficient operation and/or damage to various components in the engine. During the exhaust stroke, the burned gases in the combustion chamber must be efficiently evacuated from the combustion chamber.
Some known internal combustion engines use poppet valves to control the flow of gas into and out of the combustion chamber. Known poppet valves are reciprocating valves that include an elongated stem and a broadened sealing head. In use, known poppet valves open inwardly towards the combustion chamber such that the sealing head is spaced apart from a valve seat, thereby creating a flow path into or out of the combustion chamber when the valve is in the opened position. The sealing head can include an angled surface configured to contact a corresponding surface on the valve seat when the valve is in the closed position to effectively seal the combustion chamber.
The enlarged sealing head of known poppet valves, however, obstructs the flow path of the gas coming into or leaving the combustion cylinder, which can result in inefficiencies in the gas exchange process. Moreover, the enlarged sealing head can also produce vortices and other undesirable turbulence within the incoming air, which can negatively impact the combustion event. To minimize such effects, some known poppet valves are configured to travel a relatively large distance between the closed position and the opened position. Increasing the valve lift, however, results in higher parasitic losses, greater wear on the valve train, greater chance of valve-to-piston contact during engine operation, and the like.
Because the sealing head of known poppet valves extends into the combustion chamber, they are exposed to the extreme pressures and temperatures of engine combustion, which increases the likelihood that the valves will fail or leak. Exposure to combustion conditions can cause, for example, greater thermal expansion, detrimental carbon deposit build-up and the like. Moreover, such an arrangement is not conducive to servicing and/or replacing valves. In many instances, for example, the cylinder head must be removed to service or replace the valves.
To reduce the likelihood of leakage, known poppet valves are biased in the closed position using relatively stiff springs. Thus, known poppet valves are often actuated using a camshaft to produce the high forces necessary to open the valve. Known camshaft-based actuation systems, however, have limited flexibility to change the valve travel (or lift), timing and/or duration of the valve event as a function of engine operating conditions. For example, although some known camshaft-based actuation systems can change the valve opening or duration, such changes are limited because the valve events are dependent on the rotational position of the camshaft and/or the engine crankshaft. Accordingly, the valve events (i.e., the timing, duration and/or travel) are not optimized for each engine operating condition (e.g., low idle, high speed, full load, etc.), but are rather selected as a compromise that provides the desired overall performance.
Some known poppet valves are actuated using electronic actuators. Such solenoid-based actuation systems, however, often require multiple springs and/or solenoids to overcome the force of the biasing spring. Moreover, solenoid-based actuation systems require relatively high power to actuate the valves against the force of the biasing spring.
Thus, a need exists for an improved valve actuation system for an internal combustion engine and like systems and devices.